Thorn XE/D 2kW Lamp for Centurion Tank 98-1520

The 2kW Xenon lamp illustrated here was designed by Eric Beeson of the AEI Lamp & Lighting Company specifically to suit the low voltage and instant-light requirements of the Ministry of Defence for a new tank mounted searchlight.Prior to its development, the carbon arc had been the light source of preference in such applications - its very compact source working well with a large reflector to deliver a highly collimated beam of light. Incandescent lamps were popular for the smaller units, but they shared a common drawback with the carbon arc - their relatively low efficiency and hence phenomenal electricity consumption.

Mercury lamps had also been investigated for such applications, but their long-run up time posed problems for military service. British Siemens conceived a rather intriguing design that was used for a short while though - a compact source mercury arc tube concealed within a magnetically-operated shutter all in a large outer bulb. The lamp was kept simmering at a low current, and when full light output was required the current was increased, the response in luminous flux being immediate and the increased arc current resulting in a magnetic field which opened the shutter.

The xenon lamp pictured here had to be specially modified for use on the 24V DC battery circuit employed in the Centurion tank. The third auxiliary electrode was connected to a small Tesla transformer, which allowed the arc to be instantly ignited while only the standard low operating voltage was applied across the main electrodes. In common with AEI and Thorn's other Xenon lamps, the end seals are of a very intricate design employing multiple annular molybdenum foils.
Manufacturer: Thorn Lighting Ltd
Lamp Power: 2000 Watts
Lamp Current: 85 Amps
Lamp Voltage: 23.5 Volts
Cap Type: Special with cone centres Flexible Leads
Bulb Type: BTT-65
Bulb Finish: Clear Open Quartz
Electrodes: Solid Tungsten (thoriated) Zr getter on anode
Arc Length: 6.0-7.0mm
Atmosphere: Xenon
Luminous Flux: 80,000 lm (@ 100 hrs)
Luminous Efficacy: 40.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: 5600K Ra
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 2000 hours
Warm-up & Re-strike Time: Instant Instant
Burning Position: Vertical or Horizontal ± 15°
Overall Length: 315 ± 5 mm
Light Centre Length: 152.5 ± 2 mm from single electrode end
Factory: Leicester England
Date of Manufacture: Approx. 1970
Original Value: GB £151.80 (1972)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1969/70, p.CJ12-CJ13
2) Thorn Lighting Technical Data Sheet 98-201, January 1974
3) Thorn Lighting Comprehensive Price List, UK, 19th April 1972